Interface Electronic Coupling in Hierarchical FeLDH(FeCo)/Co(OH)2 Arrays for Efficient Electrocatalytic Oxygen Evolution.

Abstract

The oxygen evolution reaction (OER) with sluggish kinetics is the key half-cell reaction for several sustainable energy systems, such as electrochemical water splitting, fuel cells, and rechargeable metal-air batteries. Two-dimensional transition-metal hydroxides have good prospects for the OER. Herein, 2D hierarchical FeLDH(FeCo)/Co(OH)2 (LDH=layered double hydroxide) arrays were fabricated by growing 2D-ZIF-67 (ZIF=zeolitic imidazolate framework) on carbon cloth, transformation of 2D-ZIF-67 into Co(OH)2 , and electrodeposition of FeLDH(FeCo) on Co(OH)2 at ambient temperature. The optimized hierarchical catalyst exhibits high OER activity that requires a small overpotential of only 242 mV to drive 10 mA cm-2 (279 mV for 100 mA cm-2 ) and prolonged durability for 100 h at 20 mA cm-2 in 1 m KOH. The FeLDH(FeCo)/Co(OH)2 interfaces are observed to be the electrocatalytically active centers for the OER. The interfaces contribute to accelerating the OER kinetics owing to fast transfer of intermediate oxygen species. Furthermore, the FeCo alloy promotes electron transfer among the newly formed interfaces related to CoOOH in the OER process, which leads to improved durability. This work gives insight into the design and synthesis of hierarchical bimetallic hydroxide arrays with high OER activity and durability, as well as understanding of the origin of the OER promotion by metals and metal hydroxides.